Hereinafter, a description is made of conventional loudspeaker 111 with reference to a drawing. FIG. 13 is a sectional view of loudspeaker 111. Loudspeaker 111 includes magnetic circuit 104 of external-magnet type, frame 106, diaphragm 107, voice coil 108, and damper 109. Loudspeaker 111 may further include sub-cone 110. Alternatively, loudspeaker 111 may include a dust cap instead of sub-cone 110.
Magnetic circuit 104 includes upper plate 101, magnet 102, and lower plate 103. Upper plate 101 and lower plate 103 sandwich magnet 102 therebetween. Magnetic gap 105 is formed between the center pole provided at the central part of lower plate 103, and upper plate 101.
Upper plate 101 is joined with frame 106, which is made of resin. The circumference of frame 106 is bonded to the outer circumference of diaphragm 107 with an adhesive agent.
One end of voice coil 108 is joined with the central part of diaphragm 107. The other end of voice coil 108 is inserted into magnetic gap 105 of magnetic circuit 104. Damper 109 links frame 106 and voice coil 108, and holds voice coil 108 at the center of frame 106. The front surface of coil 108 has sub-cone 110 bonded thereonto.
Upper plate 101 has projection 101A. Projection 101A, fitted into through hole 106A provided in frame 106, makes upper plate 101 joined with frame 106. Upper plate 101 is formed by press work using a mold, for instance, and so is projection 101A.
Next, to join upper plate 101 with frame 106, projection 101A is firstly inserted into through hole 106A. Then, projection 101A is punched and transformed with the mold. In this way, upper plate 101 is joined with frame 106. Alternatively, projection 101A is crushed using a rotating jig, as in high spin method. Upper plate 101 is joined with frame 106 due to transformation of projection 101A.
Examples of information on prior art documents related to this patent application include patent literatures 1 and 2.